Use of two-photon polymerization for continuous gray-level encoding of diffractive optical elements

Generation of continuous gray levels in three-dimensional diffractive optical elements has remained a challenge with the current semiconductor microfabrication method. In this letter, the authors propose and demonstrate the use of the two-photon polymerization method for fabricating three-dimensional diffractive optical elements of continuous gray levels. This method is a mask-free and low-cost single-step process. It is shown that the multilevel-phase-encoded diffractive optical element fabricated in inorganic-organic hybrid polymer material facilitates the intensity distribution synthesis with a high diffraction efficiency approaching the theoretical limit.